Magneto-rheological fluid is one of intelligent materials. For example, viscosity of the magneto-rheological fluid may reversibly change according to intensity of externally applied magnetic field. In general, the magneto-rheological fluid refers to a non-colloidal suspension which includes micro-particles made of iron, nickel and cobalt having diameter of about several to tens of micron. The magnetic alloy particles may be dispersed in a dispersion media or fluid such as mineral oil, synthetic hydrocarbon, water, silicon oil, esterified fatty acid, and the like.
The magneto-rheological fluid has a dynamic range of rheological properties such as fluid viscosity characteristic when magnetic field is applied, and has substantial durability. In addition, the magneto-rheological fluid may be less influenced by contaminants, but it responds rapidly and reversibly to the magnetic field, for example, in about 10 sec. Therefore, the magneto-rheological fluid may have desirable applicability to various industrial fields such as vibration control system, for example, vehicle clutch, engine mount and damper, seismic device of high rise building, driving device such as robotic system. Further, compared to another controllable fluid such as electro-rheological fluid, the magneto-rheological fluid may be remarkably beneficial.
The magneto-rheological fluid, in general, has characteristics of newton fluid when magnetic field is not applied. However, when magnetic field is applied, dispersed magnetic particles form dipoles and thus form a fibrous structure aligned in a direction parallel to the applied magnetic field. Accordingly, the fibrous structure formed in the fluid increases viscosity, the increased viscosity provides shearing force which inhibits flow of the fluid or resistance to flow, thereby substantially increasing dynamic yield stress. The yield stress increases according to the magnetic field intensity applied to the fluid.
For efficient use of the magneto-rheological fluid, the magneto-rheological fluid may be required to have high yield stress and magnetic particles included in the magneto-rheological fluid are desired to be evenly distributed in a dispersion media. Further, fluid viscosity may be required to be low enough to readily return the fluid of its original state if applied magnetic field disappears. Moreover, the magneto-rheological fluid needs to have constant rheological characteristics with little change in viscosity in various temperature ranges. However, the magneto-rheological fluid may be greatly influenced on rheological behavior by sedimentation caused by gravity. In particular, the sedimentation occurs due to density differences between the magnetic particle and the dispersion media. For example, the typical magneto-rheological fluid has a density of about 7.86 g/cm3 which is much greater than density of the dispersive media of about 0.5 to 3 g/cm3. Therefore, the magnetic particle may form sedimentation in the dispersion media. Due to such sedimentation of the magnetic particles, dispersion stability of the magneto-rheological fluid may not be obtained.
In the related arts, a magneto-rheological fluid in which hydrophilic surfactant is adsorbed on magnetic particles on the water/oil emulsion surface and the magnetic particles are dispersed and a method manufacturing thereof have been developed. However, when using the hydrophilic surfactant-adsorbed magnetic particle, corrosion of magnetic particles may occur and boiling point of the magneto-rheological fluid may decrease due to characteristics of water/oil emulsion as a dispersion media.
In other examples of the related arts, a magneto-rheological fluid has been disclosed and the magneto-rheological fluid has improved dispersion stability and heat-resistance, high yield stress when applying magnetic field, low viscosity change in various temperature ranges, improved sedimentation stability and re-dispersibility. The magneto-rheological fluid may include a dispersion media comprising a mixture of hydrogenated hydrocarbon oil manufactured from mineral oil by hydrogenation and ester in a weight ratio of about 2:8 to 8:2. However, shear force thereof does not shown a satisfactory level of stress.
As such, development of a novel magneto-rheological fluid composition has been desired to prove improved dispersion stability and high shear stress.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.